Conventionally, a seat reclining device of this type disclosed in, for example, the patent document 1 has been known. The seat reclining device according to the patent document 1 includes a lower arm supported at a seat cushion side and having a plurality of pawls, each having an outer toothed portion at a tip end thereof and an upper arm rotatably supported by the lower arm and at the same time fixed to a seat back side, the upper arm being formed with a plurality of inner toothed portions each being engageable with the outer toothed portions of the pawls. The reclining angle of the seat back can be adjustable by varying the engagement position between the inner and outer toothed portions.
In the seat reclining device disclosed in the patent document 1, in order to move the plurality of pawls outwardly in a radial direction, a lock mechanism is provided which includes a rotational cam and a spiral spring for rotationally biasing the cam in a direction in which the pawls are moved outwardly in a radial direction.